SMM665B
Preliminary Information
APPLICATIONS INFORMATION (CONTINUED)
Note: Configuration writes or reads of registers 00HEX
to 0FHEX should not be performed while the SMM665B
is margining.
While the SMM665B is in the Power-off sequencing
mode the RST output is held active and the HEALTHY
output is held inactive regardless of trigger sources
(Figure 8). The Force Shutdown trigger option is also
POWER-OFF CASCADE SEQUENCING
The SMM665B can be programmed to perform Power-
off sequencing in either the same order or reverse
order of Power-on cascade sequencing.
disabled while in this mode.
Furthermore, the
SMM665B will not respond to activity on the
PWR_ON/OFF pin or to a Power-on I2C command
during Power-off sequencing mode.
FORCE SHUTDOWN
Power-off cascade sequencing can be initiated by the
PWR_ON/OFF pin, via I2C control or triggered by a
fault condition on any of the monitored inputs.
Toggling the PWR_ON/OFF pin to its inactive state will
initiate the Power-off sequence.
To enable software control of the Power-off
sequencing feature, the SMM665B offers an I2C
command to initiate Power-off sequencing regardless
of the state of the PWR_ON/OFF pin. Furthermore,
Power-off sequencing can be initiated by a fault
condition on a monitored input.
Once Power-off sequencing begins, the SMM665B will
wait a Power-off delay time (tDPOFF) for any channel in
the last sequence position (reverse order) and then
deactivate the PUP outputs for those channels. The
Power-off delay times are individually programmable
for each channel. The SMM665B will then wait until all
VMX inputs of the channels assigned to that sequence
position are below the programmed OFF thresholds.
At this point, the SMM665B will decrement to the next
sequence position and begin to timeout the Power-off
delay times for the associated channels. This process
continues until all of channels in the sequence have
turned off and are below their OFF thresholds. The
status register reveals that all sequenced channels
have turned off. The Power-off sequencing mode
ends when all sequenced supplies are below their
OFF thresholds.
The Force Shutdown operation brings all PUPX
outputs to their inactive state. This operation is used
for an emergency shutdown when there is not enough
time to sequence the supplies off.
The Force
Shutdown operation shuts off all sequenced channels
and waits for the supply voltages to drop below their
respective OFF thresholds.
A Force Shutdown operation can be initiated by any
one of four events. The first two methods for initiating
a Force Shutdown are always enabled. Simply taking
the FS pin to its active state will initiate a Force
Shutdown operation and maintain it until the pin is
brought to its inactive state. An I2C Force Shutdown
command allows the Force Shutdown operation to be
initiated via software control. This I2C Force Shutdown
command sets a volatile register bit that triggers a
Force Shutdown.
This bit is cleared after all
sequenced channels have dropped below their OFF
voltage threshold. During Power-on and Power-off
sequencing, the sequence termination timer can
initiate a Force Shutdown operation.
As described in the previous sections, the sequence
termination timer triggers a Force Shutdown operation
if it times out before the power supply voltages
surpass their voltage thresholds.
This Force
Shutdown will remain active until all sequenced power
supply channels have dropped below their OFF
voltage threshold. While the SMM665B is in ongoing
The programmable sequence termination timer can be
used to protect against a stalled Power-off sequence.
This timer resets itself at the beginning of each
sequence position. All channels in the sequence
position must go below their OFF threshold before the
sequence termination timer times out (tSTT) or the
sequence will terminate and all PUP outputs will be
switched to their inactive state. This timer has four
settings of OFF, 100ms, 200ms and 400ms. The
sequence termination timer can be disabled separately
for Power-off sequencing.
operations-monitor mode,
a
programmed fault
condition on any power supply channel or on the
12VIN or VDD inputs can trigger a Force Shutdown. A
Force Shutdown resulting from this will remain active
until all sequenced power supply channels have
dropped below their OFF voltage threshold.
Summit Microelectronics, Inc
2089 1.1 10/20/04
16
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
